The mac and the windoze can access the INTRAnet and the INTERnet through ip forwarding and ip masquerading on the linux, the default INTRAnet gateway being 8.37.192.1, the DNS server at 8.37.0.55. In my environment a socks server is used to connect the INTRAnet with the INTERnet; it is at 8.37.3.60.

A socks client by Hummingbird (which allows all appz to use the socks server for INTERnet connections) is available for Windows 9x. It is installed and works fine through the linux box.

The Mac is an older model running system 7.6.1. As far as I know, no socks client is available for it. Thus, appz which are not 'socks-aware' are not able to make INTERnet connections. I'm aware that the Mac versions of Netscape Navigator, Fetch 3.0 (ftp client), Anarchie (archie/ftp client), Microsoft Internet Explorer, etc. support socks--I want to enable EVERY network app on the Mac to use socks.

How would I set up the linux box so that any machine on the lab network (windows, mac, etc.) would _by default_ access the INTERnet through the socks server at 8.37.3.60 without having to have a socks client installed?

If a solution allows the linux box itself (as a client of the socks server) to access the INTERnet, it would be great, but its not necessary. The main thing is to allow the Mac to have full INTERnet access through the socks server.

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Assuming the Linux box is running a 2.2.x kernel with ipchains and transparent proxy support:
1. Run a small TCP proxy. The proxy should listen on _SOMEPORT_.
Socksify the proxy using the Linux socksification method you normally use (you might not have to do anything if you simply replace libraries).
2. Using ipchains redirect all TCP traffic originating from 10.0.0.3 to _SOMEPORT_. The appropriate command is:
"ipchains -I input -s 10.0.0.3 -p tcp -d ! 8.37.0.0/16 -j REDIRECT _SOMEPORT_".
I'm assuming all 8.37.* addresses are on the INTRAnet and should not be accessed through the SOCKS proxy.
If you want the mac to be able to access the linux box directly under its 10.0.0.1 address, you'll need to add a few ipchains commands - you can always access it through the 8.37.198.22 address, however.
3. Setup the mac to route through the Linux box.

This should allow TCP connections from the mac to be transparently redirected through the SOCKS server. It will not allow the mac to run any local server (e.g. FTP must be in passive mode). It also won't allow ICMP (i.e. ping won't work). It could probably be enhanced to work with UDP if you're using SOCKS v5 by using a UDP proxy similar to the TCP proxy and redirecting UDP traffic to it.

I recommend using tcpxd (http://quozl.us.netrek.org/tcpxd/tcpxd-0.4.tar.gz) as the proxy. You'll need to modify the code slightly - the proxy is currently built to redirect all incoming connections to a single host:port combination. Find out where it makes the "connect" call, and instead use the address returned by "getsockname". On redirected connections, "getsockname" will return the original destination instead of the local one.